Then it's Heimskingla you want, if you want Norwegian history. All others are obsolete, then, and it'll save you a bunch of money.
Just a reminder: The berserkers were respected in battle, NOT in society. They had berserker tendencies when they were at home, too, which caused them to be social outcasts. Many times they were not allowed to live within the village because they were so volotile. Egil was a berserker - see what that got him..tremendous respect for his scaldic art, but not accepted into society because nobody wanted to be around him unless they were off their rocker themselves, persecuted from land to land because of acts he'd committed at times when he could not control his berserker rage and so on. He suffered terribly from the loneliness, grief and sorrow this caused him. All of which he expresses with his poetry.
Other than that, I concur with Seraphim - variations on a theme, or like I said, it depends on how you define berserkers. I think later berserkers are still berserkers, just under a different name. Like I said before, you'd pretty much have to be a bit insane but, controlled insane, to be a ranger, SOG, LURP or whatever you want to call them. It's still a variation on the same theme, and to me, those guys are berserkers. I do respect them.